U.S. patent number 6,649,824 [Application Number 09/665,983] was granted by the patent office on 2003-11-18 for photoelectric conversion device and method of production thereof.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Tohru Den, Hiroshi Okura.
United States Patent |
6,649,824 |
Den , et al. |
November 18, 2003 |
**Please see images for:
( Certificate of Correction ) ** |
Photoelectric conversion device and method of production
thereof
Abstract
A photoelectric conversion device comprising at least an
electron acceptive charge transfer layer, an electron donative
charge transfer layer, and a light absorption layer existing
between the charge transfer layers, wherein either one of the
charge transfer layers comprises a semiconductor acicular crystal
layer comprising an aggregate of acicular crystals or a mixture of
an acicular crystal and another crystal, and a method of producing
the device are disclosed. Consequently, a photoelectric conversion
device being capable of smoothly carrying out transfer of electrons
and having high photoelectric conversion efficiency is
provided.
Inventors: |
Den; Tohru (Setagaya-ku,
JP), Okura; Hiroshi (Atsugi, JP) |
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
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Family
ID: |
26548453 |
Appl.
No.: |
09/665,983 |
Filed: |
September 20, 2000 |
Foreign Application Priority Data
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Sep 22, 1999 [JP] |
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11-268725 |
Jun 16, 2000 [JP] |
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2000-181747 |
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Current U.S.
Class: |
136/256; 136/250;
136/252; 136/258; 136/263; 257/43; 257/431; 257/436; 257/461;
257/E31.044; 429/111; 438/63; 438/85; 438/89; 438/97 |
Current CPC
Class: |
H01L
31/03682 (20130101); H01L 51/4226 (20130101); H01L
51/4233 (20130101); H01G 9/2036 (20130101); H01G
9/2059 (20130101); H01L 51/0086 (20130101); H01L
2251/306 (20130101); Y02E 10/546 (20130101); Y02E
10/549 (20130101) |
Current International
Class: |
H01L
31/0368 (20060101); H01L 31/036 (20060101); H01L
031/035 (); H01L 031/026 (); H01L 031/036 () |
Field of
Search: |
;136/263,256,258,252,250
;429/111 ;438/97,89,85,63 ;257/431,436,461,43 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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WO-91/16719 |
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Other References
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dye-sensitized colloidal TiO2 films," Nature, vol. 353, pp.
737-740, Oct. 24, 1991.* .
M.K. Nazeeruddin, et al., "Conversion of Light to Electricity by
cis-X.sub.2 Bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II)
Charge-Transfer Sensitizers (X=Cl.sup.31 ; Br.sup.31, I.sup.31,
CN.sup.31, and SCN.sup.-) on Nanocrystalline TiO.sub.2 Electrodes",
J. Am. Chem. Soc., vol. 115, No. 14, pp. 6382-6390 (1993). .
H Tsubomura, et al., "Dye sensitised zinc oxide:aqueous
electrolyte:platinum photocell", Nature, vol. 261, pp. 402-403
(1976). .
Christian Coddet et al., Metallography: Growth of Crichites During
Oxidation of Titanium or of the Alloy TA6V4 By Steam at High
Temperature, C.R. Acad. Sc. Paris, t. 281, Series C, pp. 507-510
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two-step replication process from anodic porous alumina", E.
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291 (3-2001) 1947-1949..
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Primary Examiner: Diamond; Alan
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Claims
What is claimed is:
1. A dye-sensitized photoelectric conversion device comprising at
least an electron acceptive charge transfer layer, an electron
donative charge transfer layer, and a light absorption layer
existing between the charge transfer layers, wherein either one of
the charge transfer layers is a semiconductor acicular crystal
layer comprising an aggregate of acicular crystals, and wherein the
acicular crystals comprise a metal oxide.
2. The dye-sensitized photoelectric conversion device according to
claim 1, wherein the diameters of the acicular crystals are 1 .mu.m
or less.
3. The dye-sensitized photoelectric conversion device according to
claim 1, wherein an aspect ratio of the acicular crystals is 5 or
more when the aspect ratio is defined as the ratio of the length to
the diameter of the acicular crystals or as the ratio of the length
of the acicular crystals to the length of a shortest line in a
transverse cross-section passing the gravity center of the acicular
crystals.
4. The dye-sensitized photoelectric conversion device according to
claim 1, wherein an aspect ratio of the acicular crystals is 10 or
more when the aspect ratio is defined as the ratio of the length to
the diameter of the acicular crystals or as the ratio of the length
of the acicular crystals to the length of a shortest line in a
transverse cross-section passing the gravity center of the acicular
crystals.
5. The dye-sensitized photoelectric conversion device according to
claim 1, wherein the semiconductor acicular crystal layer is
provided on a substrate, one end of the acicular crystals forming
the semiconductor acicular crystal layer is bonded to a principal
plane of the substrate, and the angle formed between the axial
direction of the acicular crystals and the principal plane of the
substrate is 60.degree. or more.
6. The dye-sensitized photoelectric conversion device according to
claim 1, wherein the semiconductor acicular crystal layer is
provided on a substrate with an electrode, one end of the acicular
crystals forming the semiconductor acicular crystal layer is bonded
to the electrode, and the angle formed between the axial direction
of the acicular crystals and the principal plane of the substrate
is 60.degree. or more.
7. The dye-sensitized photoelectric conversion device according to
claim 1, wherein the light absorption layer comprises a dye.
8. The dye-sensitized photoelectric conversion device according to
claim 1, wherein said either one of the charge transfer layers is
said electron acceptive charge transfer layer.
9. The dye-sensitized photoelectric conversion device according to
claim 8, wherein the acicular crystals comprise titanium oxide.
10. The dye-sensitized photoelectric conversion device according to
claim 8, wherein the acicular crystals comprise zinc oxide.
11. The dye-sensitized photoelectric conversion device according to
claim 8, wherein the acicular crystals comprise tin oxide.
12. The dye-sensitized photoelectric conversion device according to
claim 1, wherein a part of the acicular crystals exists in fine
pores of a finely porous layer having a number of fine pores.
13. A method of producing a dye-sensitized photoelectric conversion
device which comprises at least an electron acceptive charge
transfer layer, an electron donative charge transfer layer, and a
light absorption layer existing between the charge transfer layers,
the method comprising applying a solution containing acicular
crystals on a substrate, said acicular crystals comprising a metal
oxide, and firing the substrate to form a semiconductor acicular
crystal layer comprising an aggregate of acicular crystals on the
substrate and utilizing the semiconductor acicular crystal layer as
either one of the charge transfer layers.
14. A method of producing a dye-sensitized photoelectric conversion
device which comprises at least an electron acceptive charge
transfer layer, an electron donative charge transfer layer, and a
light absorption layer existing between the charge transfer layers,
the method comprising forming a semiconductor acicular crystal
layer comprising an aggregate of acicular crystals on a substrate
by a CVD process and utilizing the semiconductor acicular crystal
layer as either one of the charge transfer layers, wherein the
acicular crystals comprise a metal oxide.
15. The method of producing a dye-sensitized photoelectric
conversion device according to claim 14, comprising the steps of
providing an aluminum layer on a surface of the substrate,
anodizing the aluminum layer to form a finely porous alumina layer,
and growing the semiconductor acicular crystals through the alumina
fine pores by a CVD process.
16. A method of producing a dye-sensitized photoelectric conversion
device which comprises at least an electron acceptive charge
transfer layer, an electron donative charge transfer layer, and a
light absorption layer existing between the charge transfer layers,
the method comprising oxidizing a surface of a substrate to form a
semiconductor acicular crystal layer comprising an aggregate of
acicular crystals on the substrate and utilizing the semiconductor
acicular crystal layer as either one of the charge transfer layers,
wherein the acicular crystals comprise a metal oxide.
17. The method of producing a dye-sensitized photoelectric
conversion device according to claim 16, comprising the steps of
providing an aluminum layer on a surface of the substrate,
anodizing the aluminum layer to form a finely porous alumina layer,
and oxidizing at least a part of the substrate to grow the
semiconductor acicular crystals through the alumina fine pores.
18. The method of producing a dye-sensitized photoelectric
conversion device according to claim 16, wherein a substrate
comprising any one of titanium, zinc, and tin at least in the
surface thereof is used as the substrate.
19. The method of producing a dye-sensitized photoelectric
conversion device according to claim 13 or 16, wherein a substrate
having an electrode on the surface thereof is used as the
substrate.
20. A dye-sensitized photoelectric conversion device comprising at
least an electron acceptive charge transfer layer, an electron
donative charge transfer layer, and a light absorption layer
existing between the charge transfer layers, wherein either one of
the charge transfer layers is a semiconductor layer comprising a
mixture with two or more different morphologies or compositions and
at least one of the components of the semiconductor layer is an
acicular crystal comprising a metal oxide.
21. The dye-sensitized photoelectric conversion device according to
claim 20, wherein the diameter of the acicular crystal is 1 .mu.m
or less.
22. The dye-sensitized photoelectric conversion device according to
claim 20, wherein an aspect ratio is 5 or more when the aspect
ratio is defined as the ratio of the length to the diameter of the
acicular crystal or as the ratio of the length of the acicular
crystal to the length of a shortest line in a transverse
cross-section passing the gravity center of the acicular
crystal.
23. The dye-sensitized photoelectric conversion device according to
claim 20, wherein an aspect ratio is 10 or more when the aspect
ratio is defined as the ratio of the length to the diameter of the
acicular crystal or as the ratio of the length of the acicular
crystal to the length of a shortest line in a transverse
cross-section passing the gravity center of the acicular
crystal.
24. The dye-sensitized photoelectric conversion device according to
claim 20, wherein one end of the acicular crystal is bonded to an
electrode provided on a substrate and the angle formed between the
axial direction of the acicular crystal and the principal plane of
the substrate is 60.degree. or more.
25. The dye-sensitized photoelectric conversion device according to
claim 20, wherein a semiconductor other than the acicular crystal
in the mixture is a fine particle with a diameter of 100 nm or
less.
26. The dye-sensitized photoelectric conversion device according to
claim 25, wherein the fine particle exists on a surface of the
acicular crystal.
27. The dye-sensitized photoelectric conversion device according to
claim 20, wherein the material of the light absorption layer is a
dye.
28. The dye-sensitized photoelectric conversion device according to
claim 20, wherein the metal oxide is titanium oxide.
29. The dye-sensitized photoelectric conversion device according to
claim 20, wherein the metal oxide is zinc oxide.
30. The dye-sensitized photoelectric conversion device according to
claim 20, wherein the metal oxide is tin oxide.
31. The dye-sensitized photoelectric conversion device according to
claim 20, wherein a part of the acicular crystal exists in a fine
pore of a finely porous layer having a number of fine pores.
32. A method of producing a dye-sensitized photoelectric conversion
device which comprises at least an electron acceptive charge
transfer layer, an electron donative charge transfer layer, and a
light absorption layer existing between the charge transfer layers,
the method comprising applying a semiconductor mixture solution
comprising a semiconductor mixture with two or more different
morphologies or compositions on a substrate and firing the
substrate to form a semiconductor mixed crystal layer on the
substrate, and utilizing the semiconductor mixed crystal layer as
either one of the charge transfer layers, wherein at least one of
the components of the semiconductor mixed crystal layer is an
acicular crystal comprising a metal oxide.
33. A method of producing a dye-sensitized photoelectric conversion
device which comprises at least an electron acceptive charge
transfer layer, an electron donative charge transfer layer, and a
light absorption layer existing between the charge transfer layers,
the method comprising the steps of applying a solution containing a
semiconductor acicular crystal on a substrate and firing the
substrate to form an acicular semiconductor crystal layer, further
depositing a single substance or a mixture with a different
morphology or composition from that of the acicular crystal to the
semiconductor layer to form a semiconductor mixed crystal layer on
the substrate, and utilizing the semiconductor mixed crystal layer
as either one of the charge transfer layers, wherein the acicular
crystal comprises a metal oxide.
34. A method of producing a dye-sensitized photoelectric conversion
device which comprises at least an electron acceptive charge
transfer layer, an electron donative charge transfer layer, and a
light absorption layer existing between the charge transfer layers,
the method comprising the steps of growing an acicular crystal on a
substrate, depositing to the acicular crystal a single substance or
a mixture with a different morphology or composition from that of
the acicular crystal to form a semiconductor mixed crystal layer on
the substrate, and utilizing the semiconductor mixed crystal layer
as either one of the charge transfer layers, wherein the acicular
crystal comprises a metal oxide.
35. The method of producing a dye-sensitized photoelectric
conversion device according to claim 34, comprising the step of
growing the acicular crystal on the substrate by a CVD process.
36. The method of producing a dye-sensitized photoelectric
conversion device according to claim 35, comprising the steps of
forming an aluminum layer on a surface of the substrate, anodizing
the aluminum layer to form a finely porous alumina layer, and
growing a semiconductor acicular crystal through the fine pores of
the finely porous alumina layer by a CVD process.
37. The method of producing a dye-sensitized photoelectric
conversion device according to claim 34, comprising the step of
oxidizing a surface of the substrate to grow the acicular crystal
on the substrate.
38. The method of producing a dye-sensitized photoelectric
conversion device according to claim 37, comprising the steps of
forming an aluminum layer on the surface of the substrate,
anodizing the aluminum layer to form a finely porous alumina layer,
and oxidizing at least a part of the substrate to grow a
semiconductor acicular crystal through the fine pores of the finely
porous alumina layer.
39. The method of producing a dye-sensitized photoelectric
conversion device according to any one of claims 34 to 38, wherein
a substrate comprising any one of titanium, zinc, and tin in at
least a surface thereof is used as the substrate.
40. The method of producing a dye-sensitized photoelectric
conversion device according to any one of claims 32 to 34, wherein
a substrate having an electrode on a surface thereof is used as the
substrate.
41. A dye-sensitized photoelectric conversion device comprising a
p-type region and an n-type region, wherein either one of the
p-type region and the n-type region comprises whiskers of
TiO.sub.2, ZnO or SnO.sub.2.
42. The dye-sensitized photoelectric conversion device according to
claim 41, wherein an aspect ratio of the whiskers is 5 or more when
the aspect ratio is defined as the ratio of the length to the
diameter of the whiskers or as the ratio of the length of the
whiskers to the length of a shortest line in a traverse
cross-section passing the gravity center of the whiskers.
43. The dye-sensitized photoelectric conversion device according to
claim 41, wherein the diameters of the whiskers are 1 um or
less.
44. The dye-sensitized photoelectric conversion device according to
claim 41, wherein the shapes of the whiskers include a tetrapod
shape, a dendrite shape, or a broken line shape.
45. The dye-sensitized photoelectric conversion device according to
claim 41, wherein particles, an acicular substance or a film
substance adhere to the whiskers.
46. The dye-sensitized photoelectric conversion device according to
claim 41, further comprising a light absorption layer between the
p-type region and the n-type region.
47. A wet solar cell utilizing the dye-sensitized photoelectric
conversion device as set forth in any one of claims 41, or 42 to
46.
48. A dye-sensitized photoelectric conversion device comprising a
p-type region and an n-type region, wherein the n-type region
comprises metal oxide whiskers.
49. The dye-sensitized photoelectric conversion device according to
claim 48, wherein the metal oxide whiskers are ZnO.
50. The dye-sensitized photoelectric conversion device according to
claim 48, wherein the metal oxide whiskers are TiO.sub.2.
51. The dye-sensitized photoelectric conversion device according
claim 48, wherein the metal oxide whiskers are SnO.sub.2.
52. The dye-sensitized photoelectric conversion device according
claim 48, wherein particles, an acicular substance or a film
substance adhere to the metal oxide whiskers.
53. The dye-sensitized photoelectric conversion device according
claim 48, wherein said photoelectric conversion device is a wet
solar cell.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The prevent invention relates to a photoelectric conversion device
and a method of producing the device, and more particularly, to a
photoelectric conversion device comprising at least an electron
acceptive charge transfer layer, an electron donative charge
transfer layer, and a light absorption layer formed between these
charge transfer layers and a method of producing the device.
2. Related Background Art
A solar cell utilizing a semiconductor junction of silicon, gallium
arsenide or the like is generally known as a method of converting
light energy into electric energy. A crystal silicon solar cell and
a polycrystalline silicon solar cell utilizing a p-n junction of a
semiconductor, and an amorphous silicon solar cell utilizing a
p-i-n junction of a semiconductor have been developed for practical
application. However, since the production cost of a silicon solar
cell is relatively high and much energy is consumed in the
production process, it is necessary to use the solar cell for a
long duration in order to compensate the production cost and the
consumed energy. Especially, the high production cost interferes
with the wide use of a silicon solar cell.
On the other hand, recently, solar cells using CdTe and CuIn(Ga)Se
have been studied for practical application as second generation
thin film solar cells. Regarding the solar cells using these
materials, problems with environmental pollution and resource
consumption have been observed.
In addition to those dry type solar cells using a semiconductor
junction, there is also suggested a wet type solar cell utilizing a
photoelectric chemical reaction caused in the interface of a
semiconductor and an electrolytic solution. A metal oxide
semiconductor such as titanium oxide, tin oxide, or the like used
for the wet solar cell has an advantage of lowering solar-cell
manufacturing cost as compared with silicon, gallium arsenide, or
the like used for the foregoing dry type solar cells. Above all,
titanium oxide is expected to be a future energy conversion
material since it is excellent in both photoelectric conversion
efficiency in an ultraviolet region and stability. Since a stable
semiconductor such as titanium oxide, however, has a wide band gap
not less than 3 eV, only ultraviolet rays, which are about 4% of
sunrays, can be utilized, and the photoelectric conversion
efficiency has been insufficient.
For this reason, a photochemical cell (dye-sensitized wet type
solar cell) comprising a photoelectric semiconductor adsorbing dye
on the surface has been studied. At the beginning, a single crystal
electrode of a semiconductor was used for such a photochemical
cell. Examples of such electrode are titanium oxide, zinc oxide,
cadmium sulfide, tin oxide, or the like. Since an amount of the
coloring agent to be adsorbed on the single crystal electrode
lowered photoelectric conversion efficiency and the cost was high,
a porous semiconductor electrode was then used. Tubomura et al.
(NATURE, 261(1976) p. 402) reported that the photoelectric
conversion efficiency had been improved by adsorbing dye in a
semiconductor electrode made of a porous zinc oxide produced by
sintering a fine particle. Proposals of employing porous
semiconductor electrodes were also made in Japanese Patent
Application Laid-Open No. 10-112337 and Japanese Patent Application
Laid-Open No. 9-237641.
Graetzel et al. (J. Am. Chem. Soc. 115(1993) 6382, U.S. Pat. No.
5,350,644) also reported that performance as high as that of a
silicon solar cell was achieved by improving dye and a
semiconductor electrode. There, a ruthenium type coloring agent was
used as dye and an anatase type porous titanium oxide (TiO.sub.2)
was used as a semiconductor electrode.
FIG. 6 is a schematic cross-sectional view of a photochemical cell
using the dye-sensitized semiconductor electrode reported by
Graetzel et al. (hereafter referred to as a Graetzel type cell).
FIG. 6 shows an outline structure and functions of the cell.
In FIG. 6, 14a and 14b denote a glass substrate, 15a and 15b denote
a transparent electrode formed on a glass substrate, and 61 denotes
an anatase type porous titanium oxide semiconductor layer composed
of fine titanium oxide particles bonded to one another in a porous
state. Further, 62 denotes a light absorption layer of dye bonded
to the surface of the fine titanium oxide particles and 63 denotes
an electron donative electrolytic solution. An electrolytic
solution containing iodine ions may be employed as the electron
donative electrolytic solution.
A method of manufacturing a Graetzel type cell will be described
below.
At first, a layer of an anatase type titanium oxide fine particle
is formed on a glass substrate 14a on which a transparent electrode
15a is formed. Various kinds of formation methods are available,
and generally, formation of an approximately 10 .mu.m thick
semiconductor layer 61 of an anatase type titanium oxide fine
particle is carried out by applying a paste containing dispersed
anatase type titanium oxide fine particles with 10 to 20 .mu.m
particle diameter to a transparent electrode 15a and then firing
the paste at 350 to 500.degree. C. Such a method can provide a
layer with about 50% porosity and about a 1000 roughness factor
(practical surface area/apparent surface area), in which the fine
particles are well bonded to one another.
After that, dye is adsorbed in the produced titanium oxide layer
61. Various kinds of substances have been studied for use as dye
and generally a Ru complex is utilized. The titanium oxide layer 61
is immersed in a solution containing dye and dried to bind the
coloring agent to the surfaces of the titanium oxide fine particles
and to form a light absorption layer 62. A substance which does not
inhibit adsorption of dye in a titanium oxide layer, is capable of
dissolving dye well and is electrochemically inert even if
remaining on the surface of the electrode (the transparent
electrode and the titanium oxide) is suitable as a solvent to
dissolve the coloring agent, and from that point, ethanol and
acetonitrile are preferably used.
Further, as an opposed electrode, a glass substrate 14b on which a
transparent electrode 15b is formed is made ready and an ultra thin
film of platinum or graphite is formed on the surface of the
transparent electrode 15b. The ultra thin film works as a catalyst
at the time of transporting electric charge to and from an
electrolytic solution 63.
After that, while the transparent electrode 15a and 15b being set
in the inner sides, the glass substrates 14a and 14b are overlaid
as to hold the electrolytic solution 63 between them to give a
Graetzel type cell. Acetonitrile, propylene carbonate, or the like,
which are electrochemically inert and capable of dissolving a
sufficient amount of an electrolytic substance, are preferably used
as a solvent for the electrolytic solution 63. As an electrolytic
substance, a stable redox pair such as I.sup.- /I.sub.3.sup.-,
Br.sup.- /Br.sub.3.sup.- is preferably used. At the time of
forming, for example, a pair of I.sup.- /I.sub.3.sup.-, a mixture
of iodine ammonium salt and iodine, is used as a solute of the
electrolytic solution 63.
Finally, it is preferable to seal the obtained cell with an
adhesive to provide durability.
Next, the action principle of the Graetzel type cell will be
described below. Light is radiated to the Graetzel type cell from
the left side shown in FIG. 6. Subsequently, electrons of the
coloring agent constituting the light absorption layer 62 are
excited owing to the incident light. The excited electrons are
efficiently injected to the titanium oxide layer 61 and transferred
to a conduction band of titanium oxide. The coloring agent which
loses electrons and falls into an oxidized state is quickly reduced
by receiving electrons from iodine ions in the electrolytic
solution 63 and is returned to its original state. The electrons
injected into the titanium oxide layer 61 are moved owing to a
mechanism such as hopping conduction among the titanium oxide fine
particles and reach the anode 15a (the left side transparent
electrode in FIG. 6). On the other hand, the iodine ions which are
in oxidized state (I.sub.3.sup.-) by supplying electrons to the
coloring agent are reduced by receiving electrons from the cathode
(the right side transparent electrode in FIG. 6) 15b and turn back
to their original state (I.sup.-).
As is suggested by such an action principle, in order to
efficiently separate the electrons and the holes generated in the
coloring agent and move them, the energy level of the electrons of
the coloring agent in the excited state has to be higher than that
of the conduction band of titanium oxide, and the energy level of
the holes of the coloring agent has to be lower than the redox
level of iodine ion.
Further improvements on the photoelectric conversion efficiency,
the short circuit current, the open circuit voltage, the filter
factor, and durability are desirable to promote replacement of a
silicon solar cell with such a Graetzel type cell.
However, since the foregoing coloring agent-sensitized
semiconductor electrode is a titanium oxide film produced by
applying the solution containing dispersed titanium oxide fine
particles to the transparent conductive film (the transparent
electrode) 15a and sintering at high temperature after drying, the
excited electrons tend to be scattered in the interfaces of the
transparent electrode, in the titanium oxide fine particles and in
the interfaces of titanium oxide fine particles themselves. The
internal resistance generated in the interfaces of the transparent
electrode, the titanium oxide fine particles and in the interfaces
of titanium oxide fine particles themselves, therefore, is
increased to result in a decrease in photoelectric conversion
efficiency. Moreover, movement of the excited electrons to the
redox system or the like in the interfaces of the titanium oxide
fine particles themselves also causes decrease of the photoelectric
conversion efficiency.
Further, since the foregoing coloring agent-sensitized
semiconductor electrode comprises a sintered body of titanium oxide
fine particles, problems are caused, such as, adsorption of dye in
the titanium oxide fine particles located in the periphery of the
transparent electrode takes a long time, and diffusion of ions in
the electrolytic solution 63 is slow.
SUMMARY OF THE INVENTION
An object of the present invention is, therefore, to provide a
photoelectric conversion device capable of smoothly supplying and
receiving electrons and having high photoelectric conversion
efficiency.
Another object of the present invention is to provide a
photoelectric conversion device comprising a semiconductor
electrode in which electrons, holes, and ions in a light absorption
layer containing dye and a charge transfer layer containing an
electrolytic solution move best and thus the light absorption layer
and the charge transfer layer have excellent diffusion properties
during production.
Another object of the present invention is to provide a method of
producing a photoelectric conversion device having such
characteristics.
The present invention, therefore, provides a photoelectric
conversion device comprising at least an electron acceptive charge
transfer layer, an electron donative charge transfer layer, and a
light absorption layer existing between the charge transfer layers,
wherein either one of the charge transfer layers is a semiconductor
acicular (or needle) crystal layer comprising aggregate of acicular
crystals.
The present invention further provides a method of producing a
photoelectric conversion device which comprises at least an
electron acceptive charge transfer layer, an electron donative
charge transfer layer, and a light absorption layer existing
between the charge transfer layers, the method comprising applying
a solution containing acicular crystals on a substrate and firing
the substrate to form a semiconductor acicular crystal layer
comprising aggregate of acicular crystal on the substrate and
utilizing the semiconductor acicular crystal layer as either one of
the charge transfer layers.
The present invention further provides a method of producing a
photoelectric conversion device which comprises at least an
electron acceptive charge transfer layer, an electron donative
charge transfer layer, and a light absorption layer existing
between the charge transfer layers, the method comprising forming a
semiconductor acicular crystal layer comprising aggregate of
acicular crystals on a substrate by a CVD process and utilizing the
semiconductor acicular crystal layer as either one of the charge
transfer layers.
Moreover, a photoelectric conversion device comprising at least an
electron acceptive charge transfer layer, an electron donative
charge transfer layer, and a light absorption layer existing
between the charge transfer layers, wherein either one of the
charge transfer layers is a semiconductor layer comprising a
mixture with two or more kinds of different morphologies (or
configurations) or compositions and at least one of the kinds of
the semiconductor layer is an acicular crystal.
The method of producing one of the photoelectric conversion devices
of the present invention is a method of producing a photoelectric
conversion device which comprises at least an electron acceptive
charge transfer layer, an electron donative charge transfer layer,
and a light absorption layer existing between the charge transfer
layers, the method comprising applying a semiconductor mixture
solution comprising a semiconductor mixture with two or more kinds
of different morphologies or compositions on a substrate and firing
the substrate to form a semiconductor mixed crystal layer on the
substrate, and utilizing the semiconductor mixed crystal layer as
either one of the charge transfer layers.
The method of producing another one of the photoelectric conversion
devices of the present invention is a method of producing a
photoelectric conversion device which comprises at least an
electron acceptive charge transfer layer, an electron donative
charge transfer layer, and a light absorption layer existing
between the charge transfer layers, the method comprising the steps
of applying a solution containing a semiconductor acicular crystal
on a substrate and firing the substrate to form an acicular
semiconductor crystal layer, further depositing a single substance
or a mixture with a different morphology or composition from that
of the acicular crystal to the semiconductor layer to form a
semiconductor mixed crystal layer on the substrate, and utilizing
the semiconductor mixed crystal layer as either one of the charge
transfer layers.
The method of producing the other photoelectric conversion device
of the present invention is a method of producing a photoelectric
conversion device which comprises at least an electron acceptive
charge transfer layer, an electron donative charge transfer layer,
and a light absorption layer existing between the charge transfer
layers, the method comprising the steps of growing an acicular
crystal on a substrate, depositing to the acicular crystal a single
substance or a mixture with a different morphology or composition
from that of the acicular crystal to form a semiconductor mixed
crystal layer on the substrate, and utilizing the semiconductor
mixed crystal layer as either one of the charge transfer
layers.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A, 1B, 1C and 1D are outline cross-sectional views showing
photoelectric conversion devices of the present invention;
FIGS. 2A, 2B and 2C are cross-sectional views illustrating the
constitution examples of light radiation, the transparent
electrodes, and mixed crystal layers of the present invention;
FIGS. 3A, 3B, 3C and 3D are cross-sectional views illustrating the
bonding state of the mixed crystal of the present invention;
FIGS. 4A, 4B, 4C and 4D are cross-sectional views illustrating the
mixed crystals from the nanny-holes of the present invention;
FIGS. 5A, 5B, 5C and 5D are cross-sectional views illustrating the
mixed crystals from the substrate of the present invention;
FIG. 6 is a cross-sectional view of a conventional example of a
Graetzel type cell;
FIG. 7 is a simplified figure of an open-to-atmosphere type CVD
apparatus;
FIGS. 8A, 8B and 8C illustrate the structure of an acicular
crystal;
FIGS. 9A and 9B are cross-sectional views illustrating a cell
employing an acicular crystal and a mixed crystal; and
FIGS. 10A, 10B and 10C are cross-sectional views illustrating the
state of a mixed crystal;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The main characteristic of a photoelectric conversion device of the
prevent invention is that an acicular crystal is used for an
electron acceptive (n-type) or an electron donative (p-type) charge
transfer layer. The acicular crystal means so-called whisker and
preferably includes a defect-free acicular single crystal and an
acicular crystal containing screw dislocation. As illustrated in
FIGS. 8A, 8B and 8C, the acicular crystal in the present invention
also includes a crystal having a large number of acicular crystals
grown from one point as to form various shapes including a
tetrapod-like shape (FIG. 8A), a dendrite shape (FIG. 8B), and a
broken line-like shape (FIG. 8C).
Further, the acicular crystal of the present invention includes
those with all kinds of shapes such as cylindrical, conical,
conical with truncated ends, cylindrical with sharpened tips or
flat tips. Moreover, the acicular crystal includes those with
triangular pyramid, rectangular pyramid, hexagonal pyramid, and
other polygonal pyramid shapes including ones with truncated ends.
The acicular crystal also includes those with triangular prism,
rectangular prism, hexagonal prism, tip-sharpened triangular prism,
tip-sharpened rectangular prism, tip-sharpened hexagonal prism, and
other polygonal prism shapes including sharpened tip-levelled ones.
Furthermore, the crystal includes those with broken line structure
of above described shapes.
Either one of the charge transfer layers is a semiconductor layer
containing a mixture with two or more different morphologies or
with two or more different compositions, and one or more of the
semiconductor layers are a mixed crystal containing an acicular
crystal. Examples of morphology of the mixed crystal are
illustrated in FIGS. 10A, 10B and 10C. Respectively, FIG. 10A shows
an acicular crystal bearing surrounding particles. FIG. 10B shows
an acicular crystal bearing a surrounding acicular substance. FIG.
10C shows an acicular crystal bearing a surrounding film-like
substance.
In order to effectively explain the effects of an acicular crystal
and its mixed crystal, cells of the present invention will be
described while being compared with a conventional Graetzel type
cell.
FIGS. 1C and 1D are outline cross-sectional views showing
photoelectric conversion devices of the present invention. In these
FIG. 10 denotes a substrate bearing an electrode, 11b denotes an
absorption layer-modified semiconductor mixed crystal layer, 12
denotes a charge transfer layer, and 13 denotes a substrate bearing
an electrode. The substrate bearing an electrode 10 is, for
example, a glass substrate 14 on which a transparent electrode
layer 15 is formed. The absorption layer-modified semiconductor
mixed crystal layer 11 comprises a semiconductor acicular crystal
17 and a light absorption layer 16 formed on the surface of the
crystal. The semiconductor acicular crystal 17 is used as one
charge transfer layer and the light absorption layer 16 is formed
between the charge transfer layer and the other charge transfer
layer 12.
Regarding the constitution of a Photoelectric Conversion Device of
the Present Invention
In a dye-sensitized type cell represented with the foregoing
Graetzel type cell, since the light absorbency of one coloring
agent layer is insufficient, the surface area of the light
absorption layer is widened to increase the practical quantity of
absorbed light. In order to increase the surface area, a method of
dispersing and binding the fine particles may be employed, as in
the foregoing Graetzel type cell. But by this method, there occurs
the problem that the electron transfer efficiency is not
sufficient. In the foregoing Graetzel type cell, for example, the
photoelectric conversion efficiency is sometimes higher in the case
where light incidence is carried out from the side of the
transparent electrode 15a having the titanium oxide semiconductor
layer 61 than in the case where light incidence is carried out from
the opposite electrode 15a side. This not only shows the difference
of the quantity of the light according to absorbance by the
coloring agent, but also suggests according to the possibility that
electrons excited by the light absorbance which move the titanium
oxide semiconductor layer 61 and reach the transparent electrode
15a tend to be decreased more as the distance between the light
excitation position and the transparent electrode becomes greater.
In other words, it can be suggested that electrons are not
sufficiently moved in the Graetzel type cell having many crystal
grain boundaries.
An example of photoelectric conversion devices of the present
invention will be described with reference to FIGS. 1A to 1D and
FIGS. 2A to 2C.
FIG. 1A is an outline cross-sectional view showing an example of
the photoelectric conversion devices of the present invention. In
the FIGS. 10 and 13 denote substrates bearing electrodes, 11a
denotes a semiconductor acicular crystal layer having a light
absorption layer on the surface (absorption layer-modified
semiconductor acicular crystal layer), and 12 denotes a charge
transfer layer. FIG. 1B is a partly enlarged cross-sectional view
of the cross-sectional view of FIG. 1A and in the FIG. 14 denotes a
glass substrate and 15 denotes a transparent electrode and they are
equivalent to the substrate 10 bearing an electrode of FIG. 1A.
Further, 16 denotes a light absorption layer and 17 denotes a
semiconductor acicular crystal and they are equivalent to the light
absorption layer-modified semiconductor acicular crystal layer
11a.
FIGS. 1C and 1D are outline cross-sectional views showing other
examples of the photoelectric conversion devices of the present
invention. In those FIG. 10 denotes a substrate bearing an
electrode, 11b denotes an absorption layer-modified semiconductor
mixed crystal layer, 12 denotes a charge transfer layer, and 13
denotes a substrate bearing an electrode. The substrate 10 bearing
an electrode is, for example, a glass substrate 14 on which a
transparent electrode layer 15 is formed, the absorption
layer-modified semiconductor mixed crystal layer 11b comprises a
semiconductor acicular crystal 17 and a light absorption layer 16
formed on the surface. The semiconductor acicular crystal 17 works
as one of the charge transfer layers and thus the light absorption
layer 16 is to be positioned between this charge transfer layer and
the other charge transfer layer 12.
As compared with a fine particle crystal layer, the mixed crystal
layer of the present invention has a low possibility of scattering
of electrons or holes generated by photoexcitation by grain
boundaries until the electrons or holes reach a current collector.
Especially, as shown in FIG. 1D, in the case where the mixed
crystal layer is so formed as to join one end of each of the
acicular crystals to an electrode and to bond different types of
micro crystals to the acicular crystals by sintering, the effects
of grain boundaries on movement of electrons or holes are almost
completely eliminated as compared with a case of a Graetzel type
cell.
A photoelectric conversion device of the present invention
preferably comprises an acicular crystal or a mixed crystal for an
n-type wide gap semiconductor or a p-type wide gap semiconductor.
In the case where the acicular crystal or the mixed crystal is an
n-type wide gap semiconductor, a p-type wide gap semiconductor or
an electron donative charge transfer layer 12 of an electrolytic
solution containing a redox pair or of a conductive polymer is
required to be on the opposite side to the n-type wide gap
semiconductor while sandwiching a light absorption layer 16
(containing, for example, dye). On the other hand, in the case
where the acicular crystal or a mixed crystal is a p-type wide gap
semiconductor, an electron acceptive charge transfer layer 12 is
required to be on the opposite side to the p-type wide gap
semiconductor while sandwiching a light absorption layer 16.
In the case where either one of the substrates 10 or 13 bearing
electrodes is set to be a light incident plane, the electrode and
the substrate have to be transparent at least in the light incident
side. FIGS. 2A, 2B and 2C are outline cross-sectional views
illustrating practical examples of photoelectric conversion devices
of the present invention, and in the FIG. 21 denotes a glass
substrate bearing a transparent electrode, and 22 denotes an
electrode having no transmissivity (or a substrate bearing an
electrode having no transmissivity). In the constitution
illustrated in FIG. 2A, the glass substrate 21 bearing an electrode
is formed in the side of the absorption layer-modified
semiconductor acicular crystal layer 11 (the absorption
layer-modified semiconductor mixed crystal layer in the
constitutions illustrated in FIGS. 1C and 1D) to carry out light
incidence from the left side of the figures. To the contrary, in
the constitution illustrated in FIG. 2B, the glass substrate 21
bearing a transparent electrode is installed in the charge transfer
layer 12 side to carry out light incidence from the right side of
the figure. As long as the absorption or reflection of incident
light to the light absorption layer 16 can be negligible, any
constitution is applicable. Further, as illustrated in FIG. 2C, the
constitution may be such as to use the glass substrate 21 bearing a
transparent electrode for both sides and to carry out light
incidence from any side.
The constitution may optionally be selected among the exemplified
constitutions in accordance with the formation method of the
semiconductor crystal layer 11, the formation method and the
composition of the charge transfer layer 12, and so forth. In the
case where, for example, the acicular crystal layer is formed by
oxidizing a metal substrate, the acicular crystal side is
inevitably used as the electrode with no light transmissivity. On
the other hand, in the case where the acicular crystal layer is
formed by firing an acicular crystal powder, the acicular crystal
side can be employed as the glass substrate bearing a transparent
electrode. This is because the acicular crystal layer can be formed
at a relatively low temperature and the transparent electrode is
scarcely deteriorated during the acicular crystal formation
process.
FIGS. 9A and 9B are figures illustrating practical constitutions of
the foregoing acicular crystal and mixed crystal. As compared with
the Graetzel type cell shown in FIG. 6, the effects of grain
boundaries are almost completely eliminated, so that electrons and
holes can easily be moved. Further, as shown in FIG. 9B, a
semiconductor crystal 18 is adsorbed in the acicular crystal 17, so
that the effects of the grain boundaries can be suppressed and
roughness factor can be improved and, moreover, the radiated light
can reach a wide range of areas even if light is radiated to any
plane. Therefore, a large number of electrons are enabled to move
to obtain a cell of a photoelectric conversion device with high
conversion efficiency.
The mixed crystal to be employed for the present invention will be
described below.
Regarding an Acicular Crystal and a Mixed Crystal
In the case of a cell just like the foregoing Graetzel type cell
which has a light absorption layer with low absoptance per one
layer, the roughness factor is increased by using a fine particle
film with a high porosity in order to increase the surface area. On
the other hand, even in the case of using an acicular crystal, the
roughness factor can be increased if its aspect ratio is high and
the roughness factor can further be increased by sintering a micro
crystal in the surrounding of the acicular crystal.
The transverse cross-section of the acicular crystal can have
different shapes. Such as triangular, rectangular, hexagonal, or
other polygonal shape. This includes an almost round cross-section.
The respective sides may not necessarily be equal and are sometimes
different. As described before, the acicular crystal includes those
with truncated and flat ends beside those with sharpened tips. The
desirable aspect ratio of the acicular crystal is not lower than 5,
preferably not lower than 10, and further preferably not lower than
1000, though it depends on the absorptance. Additionally, the
diameter of the acicular crystal is preferably 1 .mu.m or less and
more preferably 0.1 .mu.m or less.
The aspect ratio in this case means the ratio of the length of the
acicular crystal to the diameter in the case where the acicular
crystal has a round or an approximately round transverse
cross-section and the ratio of the length to the shortest length of
a line passing the gravity center of the cross-section in the case
where the acicular crystal has a polygonal, e.g. hexagonal,
cross-section.
As a material for the acicular crystal and the mixed crystal, those
having wide energy gaps are preferable and practically, those
having 3 eV or wider energy gaps are preferable. Metal oxides are
preferable to be used as materials for the acicular crystal. As a
material for the electron acceptive (n-type) crystal, for example,
TiO.sub.2, ZnO, SnO.sub.2, or the like are preferable and as a
material for the electron donative (p-type) crystal, for example,
NiO, CuI or the like are preferable.
As a method of acicular crystal formation, a method involving
applying an acicular crystal powder and firing the powder just like
in the case of production of the foregoing Graetzel cell is
applicable. In this case, it is preferable that the acicular
crystals are approximately vertical to a substrate 14 while one end
of the acicular crystals is joined to the transparent electrode 15
as shown in FIG. 3B and FIG. 1B rather than the acicular crystals
being parallel to the substrate 14 as shown in the outline
cross-section illustrated in FIG. 3A. In addition to that, in the
case where no transparent electrode 15 exists and the substrate
works also as an electrode, one end of the acicular crystals is
preferably joined to the principal plane of the substrate. The
angle formed between the axial direction of the acicular crystals
and the principal plane of the substrate is preferably 60.degree.
or wider and more preferably 80.degree. or wider.
As a method of mixed crystal formation, the foregoing method
involving applying a mixed crystal powder and firing the powder is
applicable. In this case, it is preferable that the acicular
crystals are approximately vertical to a substrate 14 while one end
of the acicular crystals is joined to the transparent electrode 15
as shown in FIG. 3D and FIG. 1D rather than the acicular crystals
being parallel to the substrate 14 as shown in the outline
cross-section illustrated in FIG. 3C. In addition to that, the
angle formed between the axial direction of the acicular crystals
and the principal plane of the substrate is preferably 60.degree.
or wider and more preferably 80.degree. or wider. Also, there are
available the methods of applying a semiconductor crystal 18 after
being previously mixed or of applying one or more types of
semiconductor crystals first and then applying others thereon. The
semiconductor crystals 18 are preferably fine particles with 100 nm
or smaller, preferably 20 nm or smaller, diameter.
Other methods for growing an acicular crystal on an electrode such
as the transparent electrode 15 are further available. Mainly two
methods are applicable to carry out the acicular crystal growth:
one is by supplying the crystal components from the outside,
including the CVD method, PVD method, and electrodeposition method,
and the other is by causing reaction of the components of the
electrode to grow the acicular crystal.
The following are practical methods for the former: a method
involving steps of forming the undercoating electrode layer (a
metal layer) 42 on the substrate 41, as illustrated in the
cross-sectional views of FIGS. 5A and 5C, and then growing an
acicular crystal of TiO.sub.2, ZnO, or the like on the under
electrode layer 42 by open-to-atmosphere type CVD method and, in
the case of forming a mixed crystal, further depositing a
semiconductor crystal of such as TiO.sub.2, ZnO, or the like
thereon, and another method involving steps of growing an acicular
crystal of TiO.sub.2, ZnO, or the like directly on the metal
substrate 44, which works also as an under electrode, by
open-to-atmosphere type CVD method as illustrated in the
cross-sectional views of FIGS. 5B and 5D and, in the case of
forming a mixed crystal, further applying the semiconductor crystal
18 thereto.
The following are practical methods for the latter: a method
involving steps of forming the undercoating electrode layer (a
metal layer) 42 of Ti, Zn or the like on the substrate 41, as
illustrated in the cross-sectional views of FIGS. 5A and 5C, and
then growing an acicular crystal by oxidizing the surface of the
undercoating electrode layer 42 or by CVD method and another method
involving steps of growing an acicular crystal by directly
oxidizing the metal substrate 44, which works also as an under
electrode as illustrated in the cross-sectional views of FIGS. 5B
and 5D. A method of growing the acicular crystal from nano holes is
available for controlling the diameter and the growth direction of
the acicular crystal. For example, as illustrated in the
cross-sectional views of FIGS. 4A to 4D, an aluminium layer with
0.1 to 10 .mu.m thickness is formed on the undercoating electrode
layer 42 or the metal substrate 44 and a nano hole layer (a finely
porous layer) 43 of alumina is formed by anodizing the resultant
aluminium layer. The anodization is carried out using, for example,
oxalic acid, phosphoric acid, sulfuric acid, or the like. The gaps
between the neighboring nano holes can be controlled by controlling
the voltage for anodization. The diameter of the nano holes can
also be controlled by carrying out etching with a phosphoric acid
solution after the anodization. The semiconductor acicular crystal
is grown through the nano holes by gradually oxidizing the
resultant substrate 44 in an oxygen atmosphere or steam-containing
atmosphere to oxidize the undercoating electrode layer 42 or the
naked part of the metal substrate 44 after the nano hole layer 43
is formed.
In the case where the acicular crystal is grown by oxidation, the
length and the diameter can be controlled by the oxidation
conditions.
A structure where the semiconductor crystal 18 exists in the
surface of the semiconductor acicular crystal 17, as illustrated in
FIGS. 5C and 5D, can be created by forming the acicular crystal
with controlled diameter and growth direction, and after that,
immersing the resultant electrode in a gel solution containing
different types of semiconductor crystals. Consequently, even in
the case where the diameter or the length of the acicular crystal
is insufficient, a semiconductor crystal with a high roughness
factor can be produced and as a result, a semiconductor mixed
crystal with scarce effects of grain boundaries on the movement of
electrons or holes can be produced.
Regarding Light Absorption Layer
Various kinds of semiconductors and coloring agents are usable for
the light absorption layer of the photoelectric conversion devices
of the present invention. An amorphous semiconductor and a direct
transition type semiconductor with i-type and a high light
absorption coefficient are preferable for the semiconductors. A
metal complex coloring agent and/or organic and natural coloring
agents such as a polymethine coloring agent, a perylene coloring
agent, rose Bengal, Santaline coloring agent, Cyanin coloring
agent, or the like are preferable for the coloring agents. The
coloring agents preferably have proper bonding groups for forming
bonds to the surface of the semiconductor fine particle. The
preferable bonding groups are COOH group, cyano group, PO.sub.3
H.sub.2 group, and chelating groups having .PI.-conduction such as
oxime, dioxime, hydroxyquinoline, salicylate, and
.alpha.-keto-enolate. Among them, the COOH and PO.sub.3 H.sub.2
groups are especially preferable. In the case where the coloring
agent to be used for the prevent invention is a metal complex
coloring agent, a ruthenium complex coloring agent {Ru(dcbpy).sub.2
(SCN).sub.2 ; (dcbpy=2,2-bipyridine-4,4'-dicarboxylic acid) or the
likes} can be usable and it is important for the coloring agent to
have stable oxidized and reduced states.
Further, it is necessary for the electric potential of electrons
excited in the light absorption layer, that is the electric
potential (LUMO potential of dye) of dye excited by
photoexcitation, and for the electric potential of the conduction
band of the semiconductor to be higher than the electron acceptive
potential (the conduction band potential of the n-type
semiconductor) of the electron acceptive charge transfer layer and
for the electric potential of holes generated in the light
absorption layer by photoexcitation to be lower than the electron
donative potential (the valence band of the p-type semiconductor,
potential voltage of the redox pair, or the like) of the electron
donative charge transfer layer. Lowering the probability of
recombination of excited electrons and holes in the periphery of
the light absorption layer is also important in order to increase
the photoelectric conversion efficiency.
Regarding Acicular Crystal and Opposite Charge Transfer Layers
In the case where an n-type acicular crystal or a mixed crystal is
employed, a hole transfer layer is required to be formed on the
opposite side to the other charge transfer layer while sandwiching
a light absorption layer 12. On the contrary, in the case where a
p-type acicular crystal or a mixed crystal is employed, an electron
transfer layer is required to be formed as a charge transfer layer
while sandwiching a light absorption layer 12. As the charge
transfer layer, a redox type transfer layer similar to that of the
Graetzel type cell can be employed. As the redox type charge
transfer layer, not only a simple solution can be used, but also a
carrier produced from a carbon powder, a material produced by
gelling an electrolytic substance, or the like can be used. Also, a
molten salt, an ion conductive polymer, an electrochemically
polymerized organic polymer, etc. may be usable. As the hole
transfer layer, a p-type semiconductor such as CuI, CuSCN, NiO,
etc. may be used. As the electron, transfer layer, an n-type
semiconductor such as ZnO, TiO.sub.2, SnO.sub.2, etc. may be
used.
Since the charge transfer layer must be entered among the acicular
crystals or the mixed crystals, a method to be employed is the
method applicable for forming a transfer layer of a liquid or a
polymer and the plating method and CVD method applicable for
forming a solid transfer layer.
Regarding the Electrode
An electrode is so formed as to be adjacent to a charge transfer
layer and a semiconductor acicular crystal layer. The electrode may
be formed in the whole surface or a part of the surface in the
outsides of those layers. In the case where the charge transfer
layer is not a solid, the electrode is preferably formed in the
whole surface from a viewpoint of holding the charge transfer
layer. It is also preferable to form a catalyst of Pt, C, or the
like on the surface of the electrode neighboring the charge
transfer layer in order to efficiently carry out reduction of, for
example, a redox pair.
A transparent electrode made of ITO (indium tin oxide) and a tin
oxide doped with F and Sb are suitable for use as the electrode in
the light incident side. In the case where the resistance of the
layer (a charge transfer layer or a semiconductor acicular crystal
layer or a semiconductor mixed crystal layer) adjacent to the
electrode in the light incident side is sufficiently low, a partial
electrode, for example, a finger electrode or the like can be
formed as the electrode in the light incident side.
As the electrode which is not employed in the light incident side,
a metal electrode comprising of Cu, Ag, Al or the like is
preferably used.
Regarding the Substrate
The material and the thickness of a substrate are properly selected
corresponding to the durability required for a photovoltaic force
generating device. It is necessary that the substrate in the light
incident side is transparent, and a glass substrate, a plastic
substrate, or the like is suitable to be used. As the substrate
which is not employed for that in the light incident side, a metal
substrate, a ceramic substrate, or the like is suitable to be used.
It is preferable to form a reflection preventing film of SiO.sub.2
or the like on the surface of the substrate in the light incident
side.
Employing a substrate of a different material from the foregoing
electrode may be made unnecessary by using the electrode also as
the substrate.
Regarding Sealing
Though it is not illustrated in the Figs., a photoelectric
conversion device of the present invention is preferably sealed in
at least parts besides the substrates from a viewpoint of
improvement of the weathering resistance. An adhesive and resin may
be used as the sealing material. In the case where the light
incident side is sealed, the sealing material to be used has to be
transparent.
The present invention is not limited to coloring agent sensitizing
type photoelectric conversion devices but applicable widely to
photoelectric conversion devices constituted as to have a large
surface area to increase the light absorptance.
EXAMPLES
The present invention will be further described with following
examples.
Example 1
A production example of a photoelectric conversion device
comprising a semiconductor acicular crystal layer formed using a
rutile type acicular crystal powder as an electron acceptive charge
transfer layer will be described in the present example.
A slurry was produced by mixing 6 g of rutile type TiO.sub.2
crystal having 100 to 200 nm diameter and the length about 10 times
as long as the diameter (aspect ratio about 10) with 10 g of water,
0.2 g of acetylacetone, and 0.2 g of Triton X. The slurry was
applied to a conductive glass (a glass plate on which a F-doped
SnO.sub.2 film was formed) [sheet resistance 100
.OMEGA./.quadrature.] in about 50 .mu.m thickness and 1 cm.sup.2
square using a spacer, and then the resultant glass was fired at
450.degree. C. for 1 hour in oxygen gas flow at 10 sccm to obtain a
conductive glass bearing a TiO.sub.2 acicular crystal layer. The
thickness of the TiO.sub.2 semiconductor acicular crystal layer (an
electron acceptive charge transfer layer) after firing was about 10
.mu.m.
As dye, Ru(dcbpy).sub.2 (SCN).sub.2 was dissolved in distilled
ethanol and the above described conductive glass bearing the
TiO.sub.2 acicular crystal layer was immersed in the solution for
30 minutes to adsorb the coloring agent to the acicular crystal
layer, and then the conductive glass was taken out of the solution
and dried at 80.degree. C.
A mixed solution (a redox pair: I.sup.- /I.sub.3.sup.-) containing
0.46 M of tetrapropylammonium iodide and iodine (0.06 M) as a
solute and 80 vol. % of ethylene carbonate as a solvent was
produced. The solution was dropwise applied to the TiO.sub.2
acicular crystal layer of the conductive glass bearing the
TiO.sub.2 acicular crystal layer.
Another conductive glass (a glass plate on which a F-doped
SnO.sub.2 [sheet resistance 100 .OMEGA./.quadrature.] film was
formed) bearing a platinum layer of 1 nm thickness formed by
sputtering was produced, and this conductive glass and the
conductive glass bearing the TiO.sub.2 acicular crystal layer were
set on the opposite side to each other as to set the platinum layer
and the TiO.sub.2 acicular crystal layer in the inner side, and the
foregoing mixed solution was held between both glass plates to
obtain a photoelectric conversion device.
As a comparison, a photoelectric conversion device was fabricated
in the same manner except that a TiO.sub.2 powder containing
anatase type fine particles with about 20 nm particle diameter as a
main component was used.
Light was radiated from a 500 W xenon lamp equipped with a
ultraviolet-cutting filter to the side of the TiO.sub.2 acicular
crystal layer-bearing conductive glass of the respective devices
and the values of the photoelectric current were measured. In the
same manner, light was radiated to the side of the platinum
layer-bearing conductive glass of the devices and the values of
photoelectric current by photoelectric conversion reaction were
measured. As a result, the open-circuit voltage and the fill factor
of the device of the present invention were both higher by about 5%
than those of the device of the comparison in the case of radiating
light to the devices from the side of the conductive glass bearing
the TiO.sub.2 acicular crystal layer and both by about 7% in the
case of radiating light to the devices from the side of the
conductive layer bearing the platinum layer. The difference is
supposedly attributed to the decrease of the internal resistance of
the electron acceptor-type charge transfer layer owing to use of
the acicular crystals.
Example 2
A device using a ZnO acicular crystal and a device using a
SnO.sub.2 acicular crystal instead of the TiO.sub.2 acicular
crystal were fabricated. The diameter of the ZnO acicular crystal
used for the present invention was about 50 nm and the length was
about 5 times as long as the diameter. The diameter of the
SnO.sub.2 acicular crystal used was about 300 nm and the length was
about 10 times as long as the diameter. The same method of
producing the device of Example 1 was applied for the respective
production methods and the same evaluation method of Example 1 was
carried out. As a result, the open-circuit voltage values and the
fill factors of both devices were both higher by about 3% than
those of the devices of comparison (a device using a ZnO powder and
a device using a SnO.sub.2 powder) in the case of radiating the
light from the side of the conductive glass bearing the acicular
crystal layer, and both of the open-circuit voltage values and the
fill factors were higher by about 5% in the case of radiating the
light from the side of the conductive glass bearing the platinum
layer.
Example 3
A production example of a photoelectric conversion device
comprising a semiconductor acicular crystal layer formed by
oxidizing a metal material will be described with reference of
FIGS. 5A to 5D in the present example.
A substrate was produced by forming a Ti undercoating electrode
layer 42 of 3 .mu.m thickness on a quartz substrate 41, and a Ti
substrate (a metal substrate) 44 was produced, and the respective
substrates were immersed in a 0.3 M oxalic acid and 40 V voltage
was applied to slightly anodize the Ti surface. The resultant
substrates were fired at 700.degree. C. for 10 hours in He gas
current containing 10 ppm of oxygen at 100 sccm flow speed. Rutile
type TiO.sub.2 acicular crystals were grown from the undercoating
metal layer and the substrate on the Ti undercoating metal layer 42
and the Ti substrate 44 after firing as illustrated in FIGS. 5A and
5B. The diameter of the TiO.sub.2 acicular crystals was 0.1 to 1
.mu.m and the length was 10 to 100 times as long as the
diameter.
The same coloring agent as that used for Example 1 was adsorbed in
the surface of the acicular crystals in the same manner as that of
Example 1, and a photoelectric conversion device was fabricated in
the same manner as that of Example 1, except that a conductive
glass (a glass plate on which a F-doped SnO.sub.2 (sheet resistance
100 .OMEGA./.quadrature.) film was formed) bearing a graphite layer
(about 1 nm thickness) was used instead of the conductive glass
bearing the platinum layer.
As a comparison, a photoelectric conversion device was fabricated
in the same manner using a TiO.sub.2 powder containing anatase type
fine particles with about a 20 nm particle diameter as a main
component.
The photoelectric current value was measured in the same manner as
that for Example 1. The light incidence was carried out from the
side of the conductive glass bearing the graphite layer. As a
result, the open-circuit voltage and the fill factor of the device
of the present example were both higher by about 10% than those of
the device of the comparison. The difference is supposedly
attributed to the decrease of the internal resistance of the
electron acceptor-type charge transfer layer owing to use of the
acicular crystals.
Example 4
A production example of a photoelectric conversion device
comprising semiconductor acicular crystals grown from nano holes by
oxidizing a metal material will be described with reference to
FIGS. 4A to 4D in the present example.
A substrate was produced by forming a Ti undercoating electrode
layer 42 of 3 .mu.m thickness on a quartz substrate 41, and a Ti
substrate (a metal substrate) 44 was produced, and the Ti surfaces
of the respective substrates were coated with Al layers with 0.5
.mu.m thickness. Then, the respective substrates were immersed in a
0.3 M oxalic acid and 40 V voltage was applied to slightly anodize
the Ti surfaces. After that, the respective substrates were
immersed in 5 wt. % phosphoric acid for 40 minutes. By that
treatment, nano hole layers 43 having a large number of nano holes
with about 50 nm diameter at about 100 nm gaps were formed on the
alumina layers formed by anodization. The resultant substrates were
then fired at 700.degree. C. for 10 hours in He gas current
containing 10 ppm of oxygen at 100 sccm flow speed. Rutile type
TiO.sub.2 acicular crystals were grown in the Ti undercoating metal
layer 42 and the Ti substrate 44 after firing as illustrated in
FIGS. 5A and 5B. The diameter of the TiO.sub.2 acicular crystals
was 0.02 to 0.05 .mu.m and the length was 20 to 500 times as long
as the diameter.
The same coloring agent as that used for Example 3 was adsorbed in
the surface of the acicular crystals in the same manner as that of
Example 3, and a photoelectric conversion device was fabricated in
the same manner as that of Example 3.
As a comparison, a photoelectric conversion device was fabricated
in the same manner using a TiO.sub.2 powder containing anatase type
fine particles with about 20 nm particle diameter as a main
component.
The photoelectric current value was measured in the same manner as
for Example 1. The light incidence was carried out from the side of
the conductive glass bearing the graphite layer. As a result, the
open-circuit voltage and the fill factor of the device of the
present example were both higher by about 15% than those of the
device of the comparison. The difference is supposedly attributed
to the decrease of the internal resistance of the electron
acceptor-type charge transfer layer owing to use of the acicular
crystals. Moreover, it is supposedly attributed to the high aspect
ratio and the roughness factor improvement of the acicular
crystals.
Example 5
A production example of a photoelectric conversion device
comprising semiconductor acicular crystal layers grown using an
open-to-atmosphere type CVD will be described with reference to
FIGS. 5A to 5D and FIG. 7 in the present example.
FIG. 7 illustrates a simplified figure of an open-to-atmosphere
type CD apparatus employed for the present example and in the
Figure, 71 denotes a nitrogen bomb, 72 a flow meter, 73 a raw
material evaporator, 74 a nozzle, 75 an object substrate to be
treated, and 76 a substrate heating stand.
A substrate was produced by forming an Al undercoating electrode
layer 42 of 3 .mu.m thickness on a quartz substrate 41, and an Al
substrate (a metal substrate) 44 was produced, and the substrates
75 as object substrates to be treated were respectively set on the
substrate heating stand 76 of the CVD apparatus. Then,
bisacetylacetonatozinc (II) in solid phase was put in the raw
material evaporator 73 and evaporated by heat at 115.degree. C.
While the flow rate was being controlled by the flow meter 72,
nitrogen gas was supplied from the nitrogen bomb 71 to the
apparatus and the evaporated bisacetylacetonatozinc (II) was
sprayed to the substrates 75 from the nozzle 74. By such a
treatment, ZnO acicular crystals were grown from the undercoating
electrode layer and the substrate on the surface of Al undercoating
electrode layer 42 and on the surface of the Al substrate 44 as
illustrated in FIGS. 5A, 5B. The diameter of the ZnO acicular
crystals was about 1 .mu.m and the length was 10 to 100 times as
long as the diameter.
The same coloring agent as that used for Example 3was adsorbed in
the surface of the acicular crystals in the same manner as that of
Example 3, and a photoelectric conversion device was fabricated in
the same manner as that of Example 3.
As a comparison, a photoelectric conversion device was fabricated
in the same manner using a thermally treated ZnO powder with about
a 1 .mu.m particle diameter.
The photoelectric current value was measured in the same manner as
that for Example 1. The light incidence was carried out from the
side of the conductive glass bearing the graphite layer. As a
result, the open-circuit voltage and the fill factor of the device
of the present example were both higher by about 20% than those of
the device of the comparison. The difference is supposedly
attributed to the decrease of the internal resistance of the
electron acceptor-type charge transfer layer owing to use of the
acicular crystals. Moreover, it is supposedly attributed to the
high aspect ratio and the roughness factor improvement of the
acicular crystals.
Also, in the case where a ZnO layer and an Al layer were formed on
Ti substrates to obtain the object substrates 75 to be treated and
then alumina nano holes were formed in the same manner as that of
Example 4, ZnO acicular crystals were found grown through the
alumina nano holes from the ZnO layer and a photoelectric
conversion device fabricated using the substrates had open-circuit
voltage and fill factor both higher by about 20% than those of a
device of comparison.
Example 6
A production example of a photoelectric conversion device
comprising semiconductor acicular crystal layers grown using an
open-to-atmosphere type CVD, as in Example 5, will be described
with reference to FIGS. 5A to 5D and FIG. 7 in the present
example.
As an object substrate 75 to be treated, a glass plate 41 on which
a F-doped SnO.sub.2 layer 42 (sheet resistance 10
.OMEGA./.quadrature.) was formed was employed, and ZnO acicular
crystals were grown on the SnO.sub.2 layer 42 in the same manner as
that of Example 5. The diameter of the ZnO acicular crystals was
about 1 .mu.m and the length was 10 to 100 times as long as the
diameter.
After that, a photoelectric conversion device was fabricated in the
same manner as that of Example 5, except that CuI, which is a
p-type semiconductor, was employed for the charge transfer layer
12. CuI was dissolved in anhydrous acetonitrile and deposited on
the surface of a mesoscopic ZnO layer (an acicular crystal layer)
bearing dye. The substrate 41 bearing the charge transfer layer 12
was overlaid on the conductive glass bearing the graphite layer to
give a solid chemical solar cell (a photoelectric conversion
device).
A photoelectric conversion device was fabricated using a thermally
treated ZnO powder with about 1 .mu.m particle diameter in the same
manner for comparison.
The photoelectric current value was measured in the same manner as
that for Example 1. The light incidence was carried out from the
side of the conductive glass bearing the graphite layer. As a
result, the open-circuit voltage and the fill factor of the device
of the present example were both higher by about 20% than those of
the device of the comparison. The difference is supposedly
attributed to the decrease of the internal resistance of the
electron acceptor-type charge transfer layer owing to use of the
acicular crystals. Moreover, it is supposedly attributed to the
high aspect ratio and the roughness factor improvement of the
acicular crystals.
Example 7
A production example of a photoelectric conversion device
comprising an electron acceptive charge transfer layer formed using
a rutile type acicular crystal powder will be described in the
present example.
A slurry was produced by mixing 3 g of rutile type TiO.sub.2
acicular crystal having 200 to 300 nm diameter and the length about
10 times as long as the diameter and 3 g of anatase type TiO.sub.2
micro crystal (P25) having about a 20 nm diameter with 10 mL
(milliliter) of water, 0.2 mL of acetylacetone, and 0.2 mL of
Triton X (registered trade name: produced by Union Carbide Corp.).
The slurry was applied to a conductive glass (F-doped SnO.sub.2 l
100 .OMEGA./.quadrature.) in about 50 .mu.m thickness and 1
cm.sup.2 square using a spacer and then the resultant glass was
fired at 450.degree. C. for 1 hour in oxygen gas flow at 100 mL/min
(sccm).
The thickness of the obtained TiO.sub.2 acicular crystal layer
after firing was about 10 .mu.m. Ru((bipy).sub.2 (COOH).sub.2
(SCN).sub.2), which was a Ru complex salt reported by Graetzel, was
used as dye. The coloring agent was dissolved in distilled ethanol,
and the TiO.sub.2 electrode was immersed in the resultant solution
for 120 minutes to adsorb the coloring agent to the electrode, and
then the electrode was taken out of the solution and dried at
80.degree. C. On the other hand, another conductive glass (F-doped
SnO.sub.2, 10 .OMEGA./.quadrature.) bearing a platinum layer of 1
nm thickness formed by sputtering was employed as a counterpart
electrode and I.sup.- /I.sub.3.sup.- was used as a redox pair. A
mixed solution employed for the present example contained 0.46
mol/L of tetrapropylammonium iodide and 0.06 mol/L of iodine as
solutes and 80 vol. % of ethylene carbonate and 20 vol. % of
acetonitrile as solvents. The solution was dropwise applied to the
TiO.sub.2 -bearing conductive glass, and the mixed solution was
held between the conductive glass bearing the TiO.sub.2 and the
counterpart electrode to obtain a cell.
As a comparison, a cell using only P25 was fabricated in the same
manner.
Light was radiated from a 500 W xenon lamp equipped with a
ultraviolet-cutting filter to the side of the conductive glass
bearing TiO.sub.2 or to the side of the counterpart electrode. The
values of the photoelectric current generated at that time by the
photoelectric conversion reaction were measured. As a result, the
open-circuit voltage and the fill factor of the cell of the present
invention were both higher by about 5% than those of the cell of
the comparison and, especially in the case of radiating light to
the cells from the counterpart electrodes, both were higher by
about 7%. The difference is supposedly attributed to the decrease
of the internal resistance of the electron acceptor-type charge
transfer layer owing to use of the mixed crystal.
Example 8
Similar experiments to that of Example 7 were carried out using a
ZnO acicular crystal and a SnO.sub.2 acicular crystal,
respectively, instead of the TiO.sub.2 acicular crystal.
The ZnO acicular crystal used for the present invention had a
tetrapod-like shape, a diameter of about 1 .mu.m, and a length
about 5 times as long as the diameter, and the SnO.sub.2 acicular
crystal used had a diameter of about 0.5 .mu.m and a length about
10 times as long as the diameter. The same method of producing the
device of Example 7 was applied for the respective production
methods, and the same evaluation method as that of Example 1 was
carried out. As a result, the open-circuit voltage values and the
fill factors of both devices were both higher by about 3% than
those of the devices of comparison (a device using a ZnO powder and
a device using a SnO.sub.2 powder) in the case of radiating the
light from the side of the conductive glass bearing the mixed
crystal, and both of the open-circuit voltage values and the fill
factors were higher by 5% or more in the case of radiating the
light from the side of the counterpart electrodes. That is
supposedly attributed to the decrease of the internal resistance of
the electron acceptor-type charge transfer layer owing to use of
the mixed crystal.
Example 9
A production example of semiconductor acicular crystals by
oxidizing a metal material will be described with reference to
FIGS. 5A to 5D in the present example.
A substrate was produced by forming a Ti undercoating electrode
layer 42 of 3 .mu.m thickness on a quartz substrate 41 and a
substrate of a Ti plate 44 was produced, and the respective Ti
surfaces were slightly anodized at 40 V voltage in 0.3 mol/L oxalic
acid. The resultant substrates were then fired at 700.degree. C.
for 10 hours in flow of He gas containing 10 ppm oxygen at 100
mL/min (sccm) flow rate. Rutile type TiO.sub.2 acicular crystals
were found on the Ti undercoating metal layer and the Ti substrate
surface after firing, growing from the substrates as illustrated in
FIGS. 5C and 5D. The diameter of the TiO.sub.2 acicular crystals
was 0.1 to 2 .mu.m, and the length was 10 to 100 times as long as
the diameter. The resultant substrates were then immersed in a
slurry produced by mixing 3 g of anatase type TiO.sub.2 micro
crystal (P25) having about a 20 nm particle diameter with 40 mL of
water, 0.2 mL of acetylacetone, and 0.2 mL of Triton X, and after
that, the substrates were again fired at 450.degree. C. for 1 hour
in oxygen gas flow at 100 mL/min (sccm). Dye was adsorbed on the
surface of the obtained acicular crystals in the same manner as
that of Example 1. On the other hand, another conductive glass
(F-doped SnO.sub.2, 10 .OMEGA./.quadrature.) bearing graphite of
about 1 nm thickness was employed as a counterpart electrode, and
I.sup.- /I.sub.3.sup.- was used as a redox pair. Same as in the
solution employed for Example 7, a mixed solution employed for the
present example contained tetrapropylammonium iodide (0.46 mol/L)
and iodine (0.06 mol/L) as solutes and ethylene carbonate (80 vol.
%) and acetonitrile (20 vol. %) as solvents. The solution was
dropwise applied to the TiO.sub.2 -bearing conductive glass, and
the mixed solution was held between the conductive glass bearing
the TiO.sub.2 and the counterpart electrode to obtain a cell.
As a comparison, a cell using only P25 was fabricated in the same
manner.
In the same manner as that of Example 7, light was radiated from a
500 W xenon lamp equipped with a ultraviolet-cutting filter from
the side of the counterpart electrode. The values of the
photoelectric current generated at that time by the photoelectric
conversion reaction were measured. As a result, the open-circuit
voltage and the fill factor of the cell of the present invention
were both higher by about 10%. That is supposedly attributed to the
decrease of the internal resistance of the electron acceptor-type
charge transfer layer owing to use of the acicular crystal.
Example 10
A production example of semiconductor acicular crystals from nano
holes by oxidizing a metal material will be described with
reference to FIGS. 4A to 4D in the present example.
A substrate was produced by forming a Ti undercoating electrode
layer 42 of 3 .mu.m thickness on a quartz substrate 41, and a
substrate of a Ti plate 44 was produced, and the respective Ti
surfaces were coated with 0.5 .mu.m thick Al films. The Al films
were anodized at 40 V voltage in 0.3 mol/L oxalic acid and then
immersed in 5 wt. % phosphoric acid for 40 minutes. By the
treatment, a large number of nano holes with about 50 nm diameter
at about 100 nm gaps were formed in the alumina layers 43 formed by
anodization. The resultant substrates were then fired at
700.degree. C. for 10 hours in He gas current containing 10 ppm of
oxygen at 100 mL/min (sccm) flow speed. Rutile type TiO.sub.2
acicular crystals 17 were found in the Ti undercoating metal layer
and the Ti substrate surface after firing as illustrated in FIGS.
4C and 4D, growing from the nano holes of the electrodes. The
diameter of the TiO.sub.2 acicular crystals was 0.02 to 0.05 .mu.m
and the length was 20 to 500 times as long as the diameter. The
resultant substrates were then immersed in a slurry produced by
mixing 3 g of anatase type TiO.sub.2 micro crystal (P25) having
about a 20 nm particle diameter with 40 mL of water, 0.2 mL of
acetylacetone, and 0.2 mL of Triton X, and after that, the
substrates were again fired at 450.degree. C. for 1 hour in oxygen
gas flow at 100 mL/min (sccm).
Further, dye was adsorbed on the surface of the obtained acicular
crystals in the same manner as that of Example 7. On the other
hand, conductive glass (F-doped SnO.sub.2, 10 .OMEGA./.quadrature.)
bearing graphite of about 1 nm thickness was employed as a
counterpart electrode and I.sup.- /I.sub.3.sup.- was used as a
redox pair. Same as in Example 1, a mixed solution containing
tetrapropylammonium iodide (0.46 mol/L) and iodine (0.06 mol/L) as
solutes and ethylene carbonate (80 vol. %) and acetonitrile (20
vol. %) as solvents was employed. The solution was dropwise applied
to the TiO.sub.2 -bearing conductive glass and the mixed solution
was held between the conductive glass bearing the TiO.sub.2 and the
counterpart electrode to obtain a cell.
As a comparison, a cell using only P25 was fabricated in the same
manner.
In the same manner as that of Example 7, light was radiated from a
500 W xenon lamp equipped with a ultraviolet-cutting filter from
the side of the counterpart electrode. The values of the
photoelectric current generated at that time by the photoelectric
conversion reaction were measured. As a result, the open-circuit
voltage and the fill factor of the cell of the present invention
were both higher by about 5%. That is supposedly attributed to the
decrease of the internal resistance of the electron acceptor-type
charge transfer layer owing to use of the acicular crystals.
Example 11
A production example of semiconductor acicular crystals using an
open-to-atmosphere type CVD method will be described with reference
to FIGS. 5A to 5D and FIG. 7 in the present example.
A substrate was produced by forming an Al undercoating electrode
layer 42 of 3 .mu.m thickness on a quartz substrate 41, and an Al
substrate 44 was produced. These substrates were respectively set
on the substrate heating stand 76 of the CVD apparatus. Then,
bisacetylacetonatozinc (II) in solid phase was put in a raw
material evaporator 73 and evaporated by heat at 115.degree. C.
While being carried with nitrogen, the evaporated
bisacetylacetonatozinc (II) was sprayed to the Al substrates 75
from a nozzle 74. After the treatment, ZnO acicular crystals were
found grown on the Al undercoating electrode layer and the Al
substrate surface as illustrated in FIGS. 5A, 5B. The diameter of
the ZnO acicular crystals was about 1 .mu.m and the length was 10
to 100 times as long as the diameter. The resultant substrates were
then immersed in a slurry-like solution produced by mixing 3 g of
rutile type TiO.sub.2 acicular crystal and 3 g of anatase type
TiO.sub.2 micro crystal (P25) having about a 20 nm diameter with 40
mL of water, 0.2 mL of acetylacetone, and 0.2 mL of Triton X, and
after that, the substrates were fired at 450.degree. C. for 1 hour
in oxygen gas flow at 100 mL/min (sccm). Then, dye was adsorbed on
the surface of the acicular crystals in the same manner as that of
Example 1. On the other hand, conductive glass (F-doped SnO.sub.2,
10 .OMEGA./.quadrature.) bearing graphite of 1 nm thickness was
employed as a counterpart electrode and I.sup.- /I.sub.3.sup.- was
used as a redox pair. Same as in Example 7, a mixed solution
containing tetrapropylammonium iodide (0.46 mol/L) and iodine (0.06
mol/L) as solutes and ethylene carbonate (80 vol. %) and
acetonitrile (20 vol. %) as solvents was employed. The solution was
dropwise applied to the ZnO-bearing conductive substrate and the
mixed solution was held between the conductive substrate bearing
the ZnO and the counterpart electrode to obtain a cell.
As a comparison, a cell using a thermally treated ZnO powder mainly
containing particles of about 1 .mu.m particle diameter was
fabricated in the same manner.
In the same manner as that of Example 7, light was radiated from a
500 W xenon lamp equipped with a ultraviolet-cutting filter from
the counterpart electrode side. The values of the photoelectric
current generated at that time by the photoelectric conversion
reaction were measured. As a result, the open-circuit voltage and
the fill factor of the cell of the present invention were both
higher by about 7%. That is supposedly attributed to the decrease
of the internal resistance of the electron acceptor-type charge
transfer layer owing to use of the acicular crystals.
Example 12
A production example of semiconductor acicular crystals using an
open-to-atmosphere type CVD method will be described with reference
to FIGS. 5A to 5D and FIG. 7 in the present example.
Conductive glass (F-doped SnO.sub.2, 10 .OMEGA./.quadrature.) was
produced by forming a F-doped SnO.sub.2 42 film on a substrate
glass 44 and the substrate was set on a substrate heating stand 76
of the CVD apparatus. Then, bisacetylacetonatozinc (II) in solid
phase was put in a raw material evaporator 73 and evaporated by
heat at 115.degree. C. While being carried with nitrogen, the
evaporated bisacetylacetonatozinc (II) was sprayed to the
conductive glass substrate 75 from a nozzle 74. After the
treatment, ZnO acicular crystals were found grown on the conductive
glass surface as illustrated in FIG. 5C. The diameter of the ZnO
acicular crystals was about 1 .mu.m, and the length was 10 to 100
times as long as the diameter. The resultant substrate was then
immersed in a slurry-like solution produced by mixing 3 g of rutile
type TiO.sub.2 acicular crystal and 3 g of anatase type TiO.sub.2
micro crystal (P25) having about a 20 nm diameter with 40 mL of
water, 0.2 mL of acetylacetone, and 0.2 mL of Triton X and after
that the substrate was fired at 450.degree. C. for 1 hour in oxygen
gas flow at 100 mL/min (sccm). Then, dye was adsorbed on the
surface of the acicular crystals in the same manner as that of
Example 1. On the other hand, conductive glass (F-doped SnO.sub.2,
10 .OMEGA./.quadrature.) bearing graphite of about 1 nm thickness
was employed as a counterpart electrode and CuI was used as a
p-type semiconductor. CuI was at first dissolved in anhydrous
acetonitrile and then deposited on the interfaces of the mesoscopic
ZnO film bearing the coloring agent. The solid electrode produced
in such a manner and the counterpart electrode were overlaid onto
each other to obtain a solid chemical solar cell.
As a comparison, a cell using a thermally treated ZnO powder mainly
containing particles of about 1 .mu.m particle diameter was
fabricated in the same manner.
In the same manner as that of Example 7, light was radiated from a
500 W xenon lamp equipped with a ultraviolet-cutting filter from
the counterpart electrode side. The values of the photoelectric
current generated at that time by the photoelectric conversion
reaction were measured. As a result, the open-circuit voltage and
the fill factor of the cell of the present invention were both
higher by about 7%. That is supposedly attributed to the decrease
of the internal resistance of the electron acceptor-type charge
transfer layer owing to use of the acicular crystals.
Example 13
A production example of a photoelectric conversion device using a
rutile type acicular crystal powder for an electron acceptive
charge transfer layer will be described in the present example.
A slurry was produced by mixing 6 g of rutile type TiO.sub.2
acicular crystal having 200 to 300 nm diameter and a length about
10 times as long as the diameter with 10 mL (milliliter) of water,
0.2 mL of acetylacetone, and 0.2 mL of Triton X. The slurry was
applied to a conductive glass (F-doped SnO.sub.2, 100
.OMEGA./.quadrature.) in about 50 .mu.m thickness and 1 cm.sup.2
square using a spacer, and then the resultant glass was fired at
450.degree. C. for 1 hour in oxygen gas flow at 100 mL/min (sccm).
The resultant substrate was then immersed in a slurry-like solution
produced by mixing 3 g of anatase type TiO.sub.2 micro crystal
(P25) having about a 20 nm diameter with 40 mL of water, 0.2 mL of
acetylacetone, and 0.2 mL of Triton X and, after that, the
substrate was fired at 450.degree. C. for 1 hour in oxygen gas flow
at 100 mL/min (sccm). Then, dye was adsorbed on the surface of the
acicular crystals in the same manner as that of Example 7. Then,
conductive glass (F-doped SnO.sub.2, 10 .OMEGA./.quadrature.)
bearing graphite of about 1 nm thickness was employed as a
counterpart electrode, and I.sup.- /I.sub.3.sup.- was used as a
redox pair. Same as in Example 7, a mixed solution containing
tetrapropylammonium iodide (0.46 mol/L) and iodine (0.06 mol/L) as
solutes and ethylene carbonate (80 vol. %) and acetonitrile (20
vol. %) as solvents was employed. The solution was dropwise applied
to the TiO.sub.2 -bearing conductive substrate and the mixed
solution was held between the conductive substrate bearing the
TiO.sub.2 and the counterpart electrode to obtain a cell.
As a comparison, a cell using only P25 was fabricated in the same
manner.
Light was radiated from a 500 W xenon lamp equipped with a
ultraviolet-cutting filter from the side of the conductive
substrate bearing the TiO.sub.2 and to the side of the counterpart
electrode. The values of the photoelectric current generated at
that time by the photoelectric conversion reaction were measured.
As a result, the open-circuit voltage and the fill factor of the
cell of the present invention were both higher by about 3% and
especially, higher by about 5% in the case where light was radiated
to the counterpart electrode side. That is supposedly attributed to
the decrease of the internal resistance of the electron
acceptor-type charge transfer layer owing to use of the acicular
crystals.
As described above, the present invention can provide a
photoelectric conversion device in which the transfer and the
movement of electrons and holes are smoothly carried out, internal
resistance and recombination probability is low, and a high
conversion efficiency can be achieved.
Also, the present invention can provide a photoelectric conversion
device comprising a semiconductor electrode provided with a light
absorption layer of dye and a charge transfer layer of an
electrolytic solution with high impregnation and movement
speed.
Further, the present invention can provide a photoelectric
conversion device with high open-circuit voltage.
Moreover, the present invention can provide a method of producing
photoelectric conversion devices provided with the foregoing
characteristics.
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